1. Technical Field
The present invention relates to the art of brake component mounting for vehicles. More particularly, the invention relates to the art of mounting brake components on mechanical spring axle/suspension systems for heavy-duty vehicles, such as tractor-trailers or semi-trailers. Still more particularly, the invention relates to an integrated brake component mounting bracket for a mechanical spring axle/suspension system, which enables the brake chamber and the cam shaft assembly to be mounted on an axle seat, desirably reducing the number of components that are welded to the axle and enabling the use of a thinner-wall axle. The use of a thinner-wall axle desirably reduces the weight and cost associated with the axle/suspension system.
2. Background Art
Heavy-duty vehicles that transport freight, for example, tractor-trailers or semi-trailers and straight trucks, include suspension assemblies that connect the axles of the vehicle to the frame of the vehicle. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience, reference herein will be made to a subframe, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle primary frames, movable subframes and non-movable subframes.
In the heavy-duty vehicle art, reference is often made to an axle/suspension system, which typically includes a pair of transversely-spaced suspension assemblies and the axle that the suspension assemblies connect to the vehicle subframe. The axle/suspension system of a heavy-duty vehicle acts to locate or fix the position of the axle and to stabilize the vehicle. More particularly, as the vehicle is traveling over-the-road, its wheels encounter road conditions that impart various forces to the axle on which the wheels are mounted, and in turn, to the suspension assemblies which are connected to and support the axle. These forces consequently act to place or create loads on the axle and the suspension assemblies. In order to minimize the detrimental effect of these forces and resulting loads on the vehicle subframe and other vehicle components as the vehicle is operating, and in turn on any cargo and/or occupants being carried by the vehicle, the axle/suspension system is designed to absorb or dampen at least some of the forces and/or resulting loads.
Two common types of heavy-duty vehicles are known in the art as dry freight vans and refrigerated vans. Dry freight vans include enclosed trailers to keep their freight dry, and are used to transport a wide variety of non-perishable consumer and industrial goods. Refrigerated vans include enclosed trailers with refrigeration systems, and typically are used to transport perishable goods. Such dry freight vans and refrigerated vans have traditionally employed axle/suspension systems that utilize mechanical spring axle/suspension assemblies. These mechanical spring axle/suspension assemblies typically include a pair of leaf spring sets or stacks that are transversely spaced and are connected to the axle. Each leaf spring stack is engineered to carry the rated vertical load of its respective axle. Ordinarily, a trailer of a dry freight or refrigerated van employs two mechanical spring axle/suspension systems at the rear of the trailer, that is, a front axle/suspension system and a rear axle/suspension system, which is a configuration that is collectively referred to in the art as a trailer tandem axle/suspension system. As is known to those skilled in the art, the front end of the trailer is supported by a separate axle/suspension system of the tractor. For the purpose of convenience, reference herein shall be made to a spring axle/suspension system with the understanding that such reference is to a trailer tandem mechanical spring axle/suspension system.
In most axle/suspension systems, it is necessary to mount components of the vehicle braking system to one or more locations on the axle/suspension system. More particularly, the axle of the axle/suspension system includes a central tube, and an axle spindle is integrally connected by any suitable means, such as welding, to each end of the central tube. A wheel end assembly is rotatably mounted, as known in the art, on each axle spindle. A brake drum is mounted on the wheel end assembly, and as will be described in greater detail below, components of the vehicle braking system are actuated to apply friction to the brake drum in order to slow or stop the vehicle. Inasmuch as each end of the axle and its associated spindle, wheel end assembly and brake drum is generally identical to the other, only one axle end and its associated spindle, wheel end assembly and brake drum will be described herein.
As known in the art, when the operator of a heavy-duty vehicle applies the vehicle brakes to slow or stop the vehicle, compressed air is communicated from an air supply source, such as a compressor and/or air tank, through air lines to a brake chamber. The brake chamber converts the air pressure into mechanical force and moves a pushrod. The pushrod in turn moves a slack adjuster, which is connected to one end of a cam shaft of a cam shaft assembly. The cam shaft assembly enables smooth, stable rotation of the cam shaft upon movement of the slack adjuster. An S-cam is mounted on the end of the cam shaft that is opposite the slack adjuster, so that rotation or turning of the cam shaft by the slack adjuster causes rotation of the S-cam. Rotation of the S-cam forces brake linings or pads to make contact with the brake drum to create friction and thus slow or stop the vehicle. In order for the brake chamber, pushrod, slack adjuster, and cam shaft to operate properly, the brake chamber and the cam shaft assembly must be mounted on a generally stable structural member near the brake drum. More particularly, mounting of the brake chamber and the cam shaft assembly on a generally stable structural member near the brake drum is necessary so that proper alignment of the brake chamber, pushrod, slack adjuster, and cam shaft is maintained, which is important for proper actuation and performance of the brake system.
In spring axle/suspension systems of the prior art, the brake chamber has been mounted on a brake chamber bracket, and the cam shaft assembly has been mounted on a cam shaft assembly mounting bracket, which is also referred to in the art as an S-cam bearing bracket. Because it is not feasible to mount the brake chamber bracket and/or the cam shaft assembly mounting bracket directly on or to a leaf spring, these brackets have been mounted on the axle in the prior art. More particularly, the leaf spring must flex to dampen forces and thus does not provide a stable structural mounting surface. In addition, because a leaf spring is formed with a metallurgical structure that enables it to flex while withstanding significant stress, attempting to mount such brackets directly on or to the leaf spring may significantly decrease the ability of the leaf spring to withstand stress. As a result, the axle central tube, which is a generally stable structural member that is relatively near the brake drum, has been used as a mounting location for the brake chamber bracket and the cam shaft assembly mounting bracket.
More particularly, the brake chamber bracket has been rigidly attached by welding to a front portion of the axle central tube just inboardly of a respective leaf spring stack. Similarly, the cam shaft assembly mounting bracket has been rigidly attached by welding to a rear portion of the axle central tube just inboardly of a respective leaf spring stack. Such prior art mounting of the brake chamber to a bracket that is in turn welded to the axle central tube, and mounting of the cam shaft assembly to a bracket that is also in turn welded to the axle central tube, has provided a generally stable structural mounting configuration that enables sufficient operation of the brake system components. However, this configuration has certain disadvantages, including a susceptibility to stress.
For example, axles typically are hollow, which desirably reduces the amount of material used to manufacture an axle, thereby decreasing manufacturing costs, and also reduces axle weight, thereby reducing vehicle fuel consumption and costs associated with operation of the vehicle. As a result, it is desirable to use an axle with the thinnest possible wall to optimize the material and weight savings.
It is known in the art that the portion of the axle central tube which is between the leaf spring stacks is a high-stress area, due to the transmission of forces and the creation of resulting loads across the axle between the leaf spring stacks during vehicle operation. When a component is welded to a hollow axle central tube, an area on the axle wall adjacent the weld is created that is generally more susceptible to stress than a non-welded area. As a result, when forces and resulting loads act upon the axle, a welded area along the axle central tube is generally more susceptible to possible damage from such forces and/or loads than a non-welded area. In order to compensate for the increased susceptibility to stress that is caused by welds, the wall thickness of the axle typically is increased, which undesirably increases the amount of material used to manufacture the axle, and also increases the weight of the axle. Thus, in the prior art, the use of a brake chamber bracket and a cam shaft assembly mounting bracket that are each welded to the axle central tube has required the use of a relatively-thick-walled axle, which undesirably increases the cost and weight of the axle.
Alternatively in the prior art, air-ride axle/suspension systems, which are different in structure and operation from spring axle/suspension systems, have employed mounting structures in which welding of the brake chamber bracket and/or the cam shaft assembly mounting bracket to the axle central tube was eliminated. However, such mounting structures cannot be employed in a spring axle/suspension system because air-ride axle/suspension systems are different in structure and operation from spring axle/suspension systems. For example, air-ride axle/suspension systems include a pair of transversely-spaced leading or trailing arm box-type beams, in which a first end of each box-type beam is connected to the vehicle subframe, and a second or opposite end of each box-type beam is connected to the axle. In the air-ride axle/suspension system prior art, welding of the brake chamber bracket and/or the cam shaft assembly mounting bracket to the axle central tube was eliminated by mounting the brake chamber and the cam shaft assembly mounting bracket directly on the box-type beam.
Due to the different structural requirements and operation of box-type beams of an air-ride axle/suspension system and leaf springs of a spring axle/suspension system, it is not feasible to attach the brake chamber bracket and the bearing bracket directly to a leaf spring. More particularly, air-ride axle/suspension systems include air springs to dampen certain forces and thus cushion the vehicle ride. As a result, each box-type beam typically is a rigid beam that is fabricated or cast and typically includes one or more sidewalls, an upper wall, and a rear wall, and is rigidly connected to the axle. As described above, in order for the brake chamber, pushrod, slack adjuster and cam shaft to operate properly, the brake chamber and the cam shaft assembly must be mounted on a generally stable structural member near the brake drum. In an air-ride axle/suspension system, the generally rigid nature of each box-type beam and its generally rigid connection to the axle enables the box beam to be used as a stable structural mounting surface for components such as the brake chamber or brake chamber bracket and the cam shaft assembly mounting bracket. In addition, since each air-ride axle/suspension system box-type beam includes one or more sidewalls, an upper wall, and a rear wall, sufficient structural surface area is provided to enable components such as the brake chamber or brake chamber bracket and the cam shaft assembly mounting bracket to be attached to the box-type beam.
In contrast, spring axle/suspension systems do not employ air springs, instead relying on the leaf springs to flex and thus dampen forces. Because the leaf springs flex during vehicle operation, they do not provide a sufficient stable structural mounting surface to enable the mounting of components such as the brake chamber or brake chamber bracket and the cam shaft assembly mounting bracket. In addition, because leaf springs are formed with a metallurgical structure that enables them to flex while withstanding significant stress, it is undesirable to attempt to mount such components or brackets on the leaf springs, as such mounting may significantly decrease the ability of the leaf springs to withstand stress.
As a result, a need has existed in the art for a brake component mounting bracket that overcomes the disadvantages of prior art systems by providing a structure that enables a brake chamber and a cam shaft assembly to be rigidly mounted on or adjacent to the axle without welding a brake chamber bracket or a cam shaft assembly mounting bracket to the vehicle axle, thereby enabling a thinner-wall axle to be used, which in turn desirably reduces the weight and cost associated with the axle/suspension system. The integrated brake component mounting bracket for a spring axle/suspension system of the present invention satisfies this need, as will be described below.